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Biomedical subjects

R Schaffer

Publications and source records attributed to R Schaffer.

At least 19 recordsLinked to original sources
PubMed1997

NIST/NCI Micronutrients Measurement Quality Assurance Program: measurement repeatabilities and reproducibilities for fat-soluble vitamin-related compounds in human sera.

The NIST/NCI Micronutrient Measurement Quality Assurance Program has conducted 33 interlaboratory comparison exercises for fat-soluble vitamin-related compounds in human sera over the past 12 years. Periodic reanalysis of lyophilized serum samples prepared from more than 70 different sera has enabled estimation of the short- and long-term measurement characteristics. Median- and interquartile-range-based statistics adequately estimate the distribution of results from laboratories that are in analytical control from total distributions that include a significant minority of outlier data. Short-term interlaboratory reproducibility standard deviations (SDs) are predictable functions of analyte concentration, with an asymptotic limit at low analyte concentration and a linear relationship at high concentrations. Long-term trends in the interlaboratory reproducibility can be estimated by standardizing the short-term SD at the observed analyte concentration to an expected SD at a given physiologically significant analyte concentration. The "average" laboratory's same-day analytical repeatability SD is about one-third of the estimated interlaboratory reproducibility; repeatability for longer periods between analyses is, on average, on better than the reproducibility. While a few exceptional laboratories have maintained excellent repeatability over the entire decade, long-term study measurements generated within a single laboratory are not generally more internally consistent than results from multiple laboratories. Enhanced and more consistently implemented intralaboratory quality control and quality assurance methods are required to further improve and maintain interlaboratory measurement comparability.

Humans↗
PubMed1996

Effects of combining propofol and alfentanil on ventilation, analgesia, sedation, and emesis in human volunteers.

BACKGROUND: Propofol and alfentanil frequently are administered together for intravenous sedation. This study investigated pharmacokinetic and pharmacodynamic interactions between propofol and alfentanil, at sedative concentrations, with specific regard to effects on ventilation, analgesia, sedation, and nausea. METHODS: Ten male volunteers underwent steady-state infusions on 3 separate days consisting of propofol alone, alfentanil alone, or a combination of the two. Target plasma concentrations for propofol were 150, 300, and 600 ng/ml for 1 h at each concentration; for alfentanil it was 40 ng/ml for 3 h. Assessment included serial measurements of (1) ventilatory function (minute ventilation, carbon dioxide production, end-tidal carbon dioxide, ventilatory response to rebreathing 7% CO2); (2) analgesia (subjective pain report in response to graded finger shock and evoked potential amplitude); (3) sedation (subjective rating, observer scores, and digit symbol substitution test); (4) nausea (visual analog scale, 0-100 mm). RESULTS: During combination treatment, propofol plasma concentration was 22% greater than during propofol alone using replicate infusion schemes (P < 0.009). End-tidal carbon dioxide was unchanged by propofol, and increased equally by alfentanil and alfentanil/propofol combined (delta end-tidal carbon dioxide 7.5 and 6.2 mmHg, respectively). Analgesia with propofol/alfentanil combined was greater than with alfentanil alone. (Pain report decreased 50% by PA vs. 28% for alfentanil, P < 0.05). Sedation was greater with propofol/alfentanil combined than with alfentanil or propofol alone (digit symbol substitution test 30 for propofol/alfentanil combined vs. 57 for alfentanil, and 46 for propofol, P < 0.05). Nausea occurred in 50% of subjects during alfentanil, but in none during propofol/alfentanil combination treatment. CONCLUSIONS: The combination of propofol and alfentanil produced greater sedation and analgesia than that with either drug alone. Propofol offset the emetic effects of alfentanil. Equivalent depression of the carbon dioxide response curve, and elevation of end-tidal carbon dioxide occurred with propofol/alfentanil combined and alfentanil.

Adult↗
PubMed1995

Antiemetic efficacy and pharmacokinetics of intravenous ondansetron infusion during chemotherapy conditioning for bone marrow transplant.

We investigated the antiemetic efficacy and safety of intravenous ondansetron infusion in the BMT setting. We conducted prospective randomized comparison trials between ondansetron at 2 dose levels and metoclopramide (MCP) plus droperidol for the prevention of chemotherapy-induced nausea and vomiting in 2 patient populations scheduled to undergo BMT. One patient population (n = 30) received CY alone, the other population (n = 30) received combination chemotherapy of Bu and CY. The CY alone group received ondansetron for 3 days, and the Bu/CY group received ondansetron for 7 days. The primary endpoints were emesis control and nausea. Secondary endpoints included acute (headache, diarrhea and sedation) and delayed (engraftment and regimen-related) side-effects. In both trials, ondansetron provided better emesis control than did MCP plus droperidol during CY administration (P = 0.009, 3-day trial; P = 0.0022, 7-day trial). There was a wide interpatient variation in serum ondansetron levels, although group averages were proportional to the dose administered. Intrapatient day-to-day variation was 10-30% and did not change significantly with concurrent CY administration. Antiemetic efficacy did not correlate with ondansetron serum levels at the doses tested. Headache incidence was similar in all groups. Sedation was highest in the MCP plus droperidol group (P = 0.048, 3-day trial; P = 0.016, 7-day trial). No statistically significant differences in engraftment or regimen-related toxicities were observed between groups in either trial. Ondansetron appears to be a safe and efficacious antiemetic during conditioning for BMT.

Aged↗
PubMed1995

History of NIST's contributions to development of standard reference materials and reference and definitive methods for clinical chemistry.

The issuance of cholesterol as a Standard Reference Material (SRM) in 1967 started the National Institute of Standards and Technology (NIST; then named the National Bureau of Standards) on a major effort to help clinical laboratories establish and improve the quality of measurements they make. NIST now issues three kinds of SRMs for that purpose: analyte samples of certified purity as primary standards, serum samples having certified analyte concentrations as accuracy controls, and materials certified for calibrating instruments. In working with clinical laboratory scientists to establish Reference Methods (RMs) for measuring the analytes, NIST developed Definitive Methods (DMs) to use for evaluating RM accuracy and then used the DMs for assigning analyte values to its SRMs. The development of SRMs and DMs is discussed.

Blood↗
PubMed1994

Pharmacology of epidural fentanyl, alfentanil, and sufentanil in volunteers.

BACKGROUND: Despite a large number of clinical investigations in postoperative patients, the pharmacology of epidural fentanyl, alfentanil, and sufentanil has not been well characterized in a human laboratory setting. In this double-blind, placebo-controlled crossover study, we evaluated analgesia and side effects produced by epidural fentanyl (30 and 100 micrograms), alfentanil (300 and 1,000 micrograms), and sufentanil (3 and 10 micrograms) in volunteers. METHODS: Each of 12 volunteers participated in four separate study sessions. The pain model was cutaneous electrical stimulation of intensity sufficient to produce a pain report of 5 on a 0-5 scale, delivered alternately to the finger and tow. Ventilatory drive, pupil size, and subjective ratings of alertness, nausea, and pruritus were measured using visual analog scales. On each study day, after baseline measurements, an epidural catheter was placed at the L2-L3 or L3-L4 interspace. Subjects received the small dose of study drug, and the tests were repeated at 2, 55, and 95 min after drug administration. Subjects then received the large dose of the same study drug, and the series of tests was repeated at 2, 55, and 95 min later. Plasma opioid concentrations were measured using gas chromatography-mass spectrometry. RESULTS: Dose-dependent analgesia was found for all study opioids. For both doses of all opioids, toe analgesia was significantly greater than finger analgesia. Epidural fentanyl and alfentanil provided greater analgesia than sufentanil at the doses investigated. Sedation, increased end-tidal carbon dioxide, and pupillary constriction occurred only after the large epidural doses of all opioids. Overall, the incidence of subjective side effects was low, but four subjects experienced pruritus after 100 micrograms fentanyl, and four were nauseated after 1,000 micrograms alfentanil. Plasma opioid concentrations were near minimum effective analgesic plasma concentrations only after larger epidural doses. CONCLUSIONS: Lumbar epidural fentanyl, alfentanil, and sufentanil produce selective lower-extremity analgesia. Low plasma opioid concentrations measured after small epidural opioid doses suggest a spinal mechanism for analgesia. Larger doses of epidural opioids result in systemic absorption and are likely to produce supraspinal analgesia and other side effects.

Adult↗
PubMed1993

NAD turnover and utilisation of metabolites for RNA synthesis in a reaction sensing the redox state of the cytochrome b6f complex in isolated chloroplasts.

NAD is normally regarded as a redox molecule or as the substrate for ADP-ribosylation reactions. In this study, we describe the rapid metabolism of NAD by Percoll-gradient-purified lettuce chloroplasts and show that the adenine moiety can be incorporated into RNA in a dark-activated reaction that senses the redox state of the cytochrome b6f complex. Isolated chloroplasts rapidly metabolised radiolabelled NAD+ to 5'-AMP (within seconds) and adenosine during a 60-min incubation in vitro; the products were analysed by high-performance liquid chromatography. No radiolabelled ADP-ribose was detected. Radioactivity was incorporated into trichloroacetic-acid-insoluble material during this period, with approximately 2-4-fold more incorporation occurring in the dark. Most of this radiolabel was rendered acid-soluble by dilute alkaline digestion at 37 degrees C, yielding an approximately equal mixture of 2'-AMP and 3'-AMP, and by RNase digestion, identifying the acid-insoluble radioactive material as RNA. Protein-bound ADP-ribose would have yielded 5'-AMP and/or oligomeric/polymeric ADP-ribose after alkali digestion. The utilisation of NAD metabolites for RNA synthesis was restricted to the thylakoid compartment of the chloroplast. The use of a variety of electron-transport inhibitors such as 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, bromanil (tetrabromo-1,4-benzoquinone), electron donors (dithiothreitol), electron acceptors (ferricyanide) and an uncoupler showed that the incorporation of radiolabel from NAD into acid-insoluble material was favoured when the cytochrome b6f complex was in the oxidised state (as pertaining to incubations in the dark).

Chloroplasts↗
PubMed1993

Behavioural mechanisms in AIDS patients under stress.

Clinical observation at the Kenyatta National Hospital showed unusually rapid deterioration of patients testing seropositive to HIV infection and being moved to a side room for nursing. This pilot study tested the hypothesis that deterioration was at least partly, mediated by B-endorphins and other endogeneous opioids. The study design was a prospective and comparative study looking at 6 HIV seropositive and 10 control (HIV seronegative) patients matched for sex, age, and clinical status at time of study. The laboratory measures compaired were baseline, and daily serum B-endorphin and ACTH. A significant variation is noted between the two groups. The significance of this study is discussed.

Adolescent↗
PubMed1993

Redistribution of sufentanil to cerebrospinal fluid and systemic circulation after epidural administration in dogs.

Due to its higher lipid solubility, sufentanil may be less likely than morphine to migrate rostrally in the cerebral spinal fluid (CSF) and cause delayed respiratory depression following epidural administration. However, early respiratory depression has been reported in patients after relatively large doses of epidural sufentanil. This has been attributed to systemic drug uptake. We used a dog model to investigate the pharmacokinetics and rostral spread of epidural sufentanil in CSF. Sampling catheters were placed in the lumbar subarachnoid space, the cisterna magna, and femoral arteries of six mongrel dogs. Samples of cisternal CSF, lumbar CSF, and blood were drawn at 0, 1, 5, 15, 30, 60, 90, 120, and 180 min after lumbar epidural sufentanil injection. We measured sufentanil concentrations by gas chromatography-mass spectrometry and used the least squares method to a fit tri-exponential function to each sufentanil concentration versus time data set. Paired t-test was used to test for statistical significance. After epidural sufentanil, lumbar CSF concentrations were significantly higher than plasma or cisternal CSF sufentanil concentrations at all assessment times. Sufentanil concentrations were significantly higher in cisternal CSF than in plasma at 30 and 60 min after injection. Sufentanil appeared rapidly in lumbar CSF, reaching a maximum concentration (Cmax) of 57 ng/mL at 6.5 min. In cisternal CSF, a Cmax of 1.2 ng/mL was reached at 21 min, and Cmax in plasma was 0.35 ng/mL at 6 min. The area under the concentration-time curve (AUC) of sufentanil in cisternal CSF was approximately six times higher than the plasma AUC (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Evaluation of the accuracy of a pharmacokinetically-based patient-controlled analgesia system.

Bone marrow transplant patients having severe, prolonged oral mucositis pain (expected to last for one to three weeks) used a computer-controlled infusion system to self-administer morphine for pain control. Individual patient pharmacokinetic information, derived from a pretreatment bolus morphine dose, was used in a new bolus-elimination transfer algorithm to produce rapid adjustments of steady plasma morphine concentrations when the patient requested more or less drug. We evaluated the performance characteristics (bias and precision) of this pharmacokinetically based patient-controlled analgesic infusion system (PKPCA) in a group of 15 cancer patients over six to 14 days. Although we found a three- to fivefold pharmacokinetic variability in the tailoring morphine dose data, the PKPCA system was free of systematic bias (insignificant overall prediction error) during the patient-controlled infusions in this study population. The absolute prediction error was 19.9% for the group on the first study day and 25.6% over the entire study period (aggregate results; 6-14 days of continuous use). Two-thirds of the patients exhibited no bias throughout the study period, and individual bias in the others was symmetrically distributed (three patients with underpredictions and two overpredicted). Magnitude of prediction error during the patient-controlled morphine infusions was not related to the magnitude of pharmacokinetic deviation of individual subjects from group parameters. Our results indicate that this PKPCA system provides accurate control of plasma morphine concentration when used by patients to self-administer opioid for prolonged pain relief continuously over 1 to 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia, Patient-Controlled↗
PubMed1991

Multiple-dose evaluation of intravenous hydromorphone pharmacokinetics in normal human subjects.

We measured the pharmacokinetics of hydromorphone in normal volunteers given three doses of the drug (10, 20, and 40 micrograms/kg) as intravenous 45-s injections on different days. Concentrations of hydromorphone in plasma from serial blood samples were measured by a high-performance liquid chromatography method specific for hydromorphone with a detection limit of 0.1 ng/mL. In all cases, plasma hydromorphone concentration versus time data for individual subjects were best described by a triexponential (instead of mono- or biexponential) function. Furthermore, we found that the pharmacokinetics of hydromorphone was independent of dose across the range studied. Averaged across doses, the distribution and terminal elimination half-lives were 1.27 min (t1/2 pi), 14.7 min (t1/2 alpha), and 184 min (t1/2 beta), respectively. Average values for systemic clearance, initial dilution volume, and steady-state volume of distribution were 1.66 L/min (Cl), 24.4 L (Vc), and 295 L (Vdss). Our results indicate that hydromorphone pharmacokinetic parameters are linear across a fourfold range of doses that are usually employed clinically and that previously reported pharmacokinetic values for hydromorphone (based on radioimmunoassay measurements) deserve reconsideration.

Adult↗
PubMed1989

The National Reference System for Cholesterol.

The NRS/CHOL is a reality that is progressively becoming the way in which accuracy of cholesterol results is being ensured. Proof of traceability to NRS/CHOL within each segment of the clinical laboratory, now an expectation, will soon be the norm that makes a sound conceptual reference system into an everyday reality that reaches into the many thousands of working sites that measure cholesterol in serum on patient samples.

Cholesterol↗
PubMed1985

Relationship of ultrasound findings after cesarean section to operative morbidity.

Postcesarean section febrile morbidity remains a common problem on obstetric services. Although a few preliminary studies have reported on the use of ultrasound to assess the postcesarean section patient, they have not compared sonographic findings with either intraoperative or postoperative events. These reports have noted fluid collections around the incision site. In this report of 100 postcesarean section patients, it is noted that echo-free areas anterior to the incision site, which correspond to the described fluid collections, were present in 29% of patients and were more frequently found in patients with excess blood loss at surgery. Patients whose echo-free areas were greater than or equal to 3.5 cm were significantly more likely to have postoperative morbidity. The significance of these findings and the role of ultrasound in the evaluation of the postcesarean section patient are discussed.

Abscess↗
PubMed1985

Candidate reference method for determination of total bilirubin in serum: development and validation.

This candidate Reference Method for measuring total bilirubin in serum is based on the Jendrassik-Gróf principle (Clin Chem 29: 297-301, 1983). Standard Reference Material no. 916 bilirubin (National Bureau of Standards) is used as the standard. Bilirubin standard solutions may be prepared either in human serum or in 40 g/L albumin solution (human or bovine), because we found the molar absorptivity of the azopigment at 598 nm to be identical in these media. The absorptivities of the unconjugated and conjugated azopigments appear to be identical, but the conjugated azopigment is completely hydrolyzed in the final reaction mixture. Bilirubin added to serum from adults or neonates was quantitatively accounted for. Interference by hemoglobin (up to 2 g/L), ascorbic acid (up to 20 mg/L), or zinc (at physiological concentrations) is negligible. Of the therapeutic drugs we tested, only L-dopa and alpha-methyldopa interfere. We established normal adult reference values for total bilirubin and examined the intraindividual variation in 19 subjects.

Adult↗
PubMed1984

Multiple pancreatic pseudocyst disease.

In an effort to determine the incidence of multiple pseudocyst disease and establish the optimal approach to this problem, the records of 91 consecutive patients diagnosed during a 36-month period as having pancreatic pseudocyst disease by sonography or computerized tomographic scanning were reviewed. Thirteen patients (14.3%) had multiple cysts; all received sonograms and six had CT scans. The combined false negative and false positive rate with sonography was 9%. Spontaneous resolution occurred involving five cysts (18%) up to 6.5 cm in size. The diagnosis of cyst multiplicity was confirmed at operation in seven cases; two of the seven operations were excisional and the remaining patients received drainage procedures. There were no operative deaths; complications included one patient who required chronic enzyme replacement therapy after excision and another patient who developed a subphrenic abscess after attempted percutaneous drainage. The incidence of multiple pseudocyst disease in our series is just over 14%. The possibility of multiplicity should be carefully investigated in each patient with pseudocyst disease. In light of the rate of spontaneous resolution, not all patients with multiple pseudocysts may require operative therapy. Because of the 7.7% false negative diagnoses with sonography, CT scanning is especially helpful when the diagnosis of multiple pseudocysts is suspected or in preoperative preparation of pseudocyst drainage. If an operation becomes necessary, a drainage procedure rather than excision should be used whenever possible to maximize gland salvage.

Adult↗